Somatic mosaicism for a deletion of the dystrophin gene in a carrier of Becker muscular dystrophy

Duchenne muscular dystrophy (DMD) and the allelic milder form of Becker muscular dystrophy (BMD) are caused by mutations of the dystrophin gene on the short arm of the X chromosome. One third of affected indviduals are expected to result from de novo mutations. Genetic counselling of families with sporadic cases is complicated by the potential meiotic origin of the mutation in the mother resulting in germline mosaicism. Here we present direct evidence for combined somatic and germline mosaicism for a deletion of the dystrophin gene, thereby proving the mitotic origin of this deletion and pinpointing a further potential pitfall for genetic counselling. The mother of a BMD son and a BMD carrier daughter, both carrying a deletion of dystrophin cDNA 7 (0.5 kb Hind III fragment) and cNDA 8, was herself clinically healthy and had normal creatine kinase levels. A muscle specimen of the mother showed mild overall pathology as well as focal dystrophin deficiency. In contrast chromosomal in situ suppression (CISS) hybridization of metaphase chromosomes using a cosmid clone of the corresponding cDNA deleted in her son revealed no evidence of somatic mosaicism in their lymphocytes. These results emphasize the value of an approach correlating genetic and immunological data for the definition of a carrier state in BMD or DMD. The possibility of somatic mosaicism should be considered when genetic counselling of a family with a sporadic case of BMD or DMD is performed.     

Deletion analysis for Duchenne (and Becker) muscular dystrophy

Forty-three unrelated South Australian boys diagnosed as having either Duchenne or Becker muscular dystrophy were screened for deletions using DNA probes to the dystrophin gene. For the 35 boys with Duchenne muscular dystrophy, the deletion frequency was 43% using a simplified probing strategy based on the probes Cf56a, Cf56b, pERT87-15 and XJ (XJ1.1 or XJ2.3). The corresponding deletion frequency for the eight boys with Becker muscular dystrophy was 38%. Members of families in which these disorders result from a deletion can now choose to prevent the birth of further affected boys, using an accurate prenatal test for the specific mutation occurring within the family. Deletion analysis also has the potential to clarify the carrier status of women in these families.     

Deletion analysis for Duchenne (and Becker) muscular dystrophy

Abstract Forty-three unrelated South Australian boys diagnosed as having either Duchenne or Becker muscular dystrophy were screened for deletions using DNA probes to the dystrophin gene. For the 35 boys with Duchenne muscular dystrophy, the deletion frequency was 43% using a simplified probing strategy based on the probes Cf56a, Cf56b, pERT87-15 and XJ (XJ1.1 or XJ2.3). The corresponding deletion frequency for the eight boys with Becker muscular dystrophy was 38%. Members of families in which these disorders result from a deletion can now choose to prevent the birth of further affected boys, using an accurate prenatal test for the specific mutation occurring within the family. Deletion analysis also has the potential to clarify the carrier status of women in these families.     

Intragenic deletions in the dystrophin gene in 211 Pakistani Duchenne muscular dystrophy patients

Background: Deletions of single or multiple exonic regions within the dystrophin gene can be detected using current molecular methods in approximately 65% of the patients with X‐linked recessive neuromuscular disorder, Duchenne/Becker muscular dystrophy (DMD/BMD). Population‐based variations in frequency and distribution of dystrophin gene deletions have been reported in DMD/BMD patients. In the present study, the first in the Pakistani population, frequency and distribution of deletions of 18 exons clustered in two hot spots within the dystrophin gene in 211 unrelated DMD patients were analyzed. Methods: A total of 211 patients suffering from DMD were ascertained, and intragenic deletions within the dystrophin gene were detected on polymerase chain reaction amplification of the genomic DNA using 18 primer sets clustered within two major deletion hot spots. lovd v.1.1.0 software from the Leiden Muscular Dystrophy website has been used to predict in‐frame and out‐of‐frame deletions. Results: Intragenic deletions were detected in 86 patients (40.75%): 35 patients (40.69%) had deletions within the proximal hot spot, and 51 patients (59.30%) had deletions confined to the distal deletion hot spot of the dystrophin gene. The most frequently deleted exons were 50, 6, 47, 13 and 52 with deletion frequencies of 15.11%, 12.79%, 10.46%, 8.13%, and 4.65%, respectively. lovd v.1.1.0 predicted out‐of‐frame deletions in 67 DMD patients and in‐frame deletions in 19 DMD patients. Conclusions: The observed proportion of intragenic deletions in the Pakistani population is relatively low, which is comparable with most of the Asian data. Also, deletions in 67 patients (77.9%) are in agreement with the frame‐shift rule.     

Deletion analysis of DMD/BMD children in Singapore using multiplex polymerase chain reaction (PCR) technique.

Twenty-three children suffering from Duchenne/Becker muscular dystrophy (DMD/BMD) in Singapore were analysed using the multiplex polymerase chain reaction (PCR) technique. Deletions were found in 14 cases. One rare case of total deletion of all nine exons was observed. This is the first DMD/BMD deletion analysis on South East Asian children. This technique for screening deletions was informative in 61 per cent of the local cases and would be useful for rapid diagnosis of deletion cases of DMD/BMD.     

Becker/Duchenne肌营养不良患儿临床表型与基因关联性预测分析

目的 探讨Becker/Duchenne肌营养不良（BMD/DMD）患儿的临床表型与基因型的关联性，为疾病的管理、基因治疗及产前诊断提供理论依据。方法 回顾性分析52例患儿的临床资料及基因检测结果，对52例患儿均采用多重连接探针扩增（MLPA）的方法检测DMD基因，对MLPA检测未发现基因异常的患儿采用外显子芯片捕获结合高通量测序技术（NGS）进行筛查；并对20例先证者的母亲进行了测序验证。结果 结合MLPA和NGS测序技术检测到50例患儿携带BMD/DMD致病基因，检出率为96%。其中，基因缺失36例（69%）、重复7例（13%）、微小突变7例（13%）。在43例存在基因缺失/重复的患儿中，DMD 32例，BMD 11例；37例（86%）符合阅读框架原则，其中DMD 27例（96%），BMD 10例（67%）。7例微小突变均为DMD。结论 阅读框架原则对DMD有极高预测价值，对BMD预测有限。     

Italian experience regarding the prevention of Duchenne and Becker muscular dystrophies

The indirect approach to carrier detection and prenatal diagnosis of Duchenne and Becker muscular dystrophies based on the study of DNA polymorphisms closely linked to this gene has been followed by five Italian laboratories in the study of 106 pedigrees. Out of 354 women studied up to 1 May 1987, 147 were identified as carriers because of pedigree information and/or of increased creatine phosphokinase (CPK) values. Of the remaining 207, 184 could be assigned to three arbitrarily defined risk categories (low, intermediate and high) using linkage analysis. This disaggregation of women at risk is clearly more useful than that defined before DNA analysis, in which the same 184 women could be assigned only to the low or intermediate risk categories. Prenatal diagnosis was theoretically possible in 90% of carrier women, and was actually performed in 14 pregnancies, which led to the identification of four affected male foetuses, one also having Down syndrome.Abbreviations DMD Duchenne muscular dystrophy - BMD Becker muscular dystrophy - CPK creatine phosphokinase - PND prenatal diagnosis     

Carrier detection by DNA analysis in Duchenne muscular dystrophy families.

We applied DNA analysis techniques to Turkish families whose members were afflicted with Duchenne/Becker muscular dystrophy. The aim of this study was to establish a prenatal diagnosis of this anomaly and to determine the carrier state. All of the techniques used in established diagnosis centers are now applied routinely in our laboratory. Both Southern analysis and polymerase chain reaction (PCR) methods were used for deletion detection in patients and restriction enzyme fragment length polymorphism (RFLP) determination for linkage analysis in women at risk. CA repeated sequence length polymorphism, the most recent technique for linkage analysis, was also applied. About 250 individuals from seventy-nine families were investigated and thirty-six entire families were screened. Twenty-five women were found to be carriers while thirty seven were non-carriers. The carrier state could not be determined in three women.     

Deletion screening and prenatal diagnosis of Duchenne muscular dystrophy using cDNA probes Cf 23a and Cf 56a

We have screened patients of 14 families at risk for Duchenne muscular dystrophy (DMD) from the northern part of the German Democratic Republic using the cDNA clones Cf 23a and CF 56a. Of the 14 unrelated DMD families, 7 (50%) showed different deletions with these cDNA probes. A prenatal diagnosis by chorionic villi sampling was performed in a DMD family with patients showing a deletion of the 5.4 kb Pst I band detected by the cDNA probe Cf 56a. This band corresponds to a 10 kb exon region of the cDNA probe 8 of Koenig et al. [12]. The patient's mother was informative only for the flanking marker 99.6. The male fetus showed the same haplotype and the same deletion as the two patients.     

Dystrophin Abnormality in Progressive Muscular Dystrophy -A Review Article-

Duchenne muscular dystrophy (DMD) is a fatal X-linked recessive disorder of muscle in children, with an incidence of approximately 1 in 3,300 male births. In about a third of affected boys, the disease is due to a new mutation, and most patients die in their early 20s. Over the last few years, the genetic, biochemical and histopathological basis of DMD has been elucidated greatly. In particular, the discovery of "dystrophin," the protein product of the DMD gene is truly an epoch-making success in the history of muscular dystrophy research. Dystrophin is now thought to be a cytoskeletal protein underlying the plasma membrane (known in muscle as the sarcolemma) of normal muscle fiber, and is undetectable or greatly reduced in DMD. In this review article, dystrophin in normal skeletal muscle and various neuromuscular diseases including DMD/BMD (Becker muscular dystrophy), and its carrier is discussed.     

脊髓性肌萎缩的基因诊断和产前基因诊断研究

目的探讨中国人脊髓性肌萎缩(SMA)基因诊断和产前基因诊断的可行性。方法应用复合聚合酶链反应-限制性片段长度多态(PCR-RFLP)方法对31例SMA患儿进行神经元存活基因(SMN)第7外显子缺失分析,并对2例有SMA阳性家族史的家系进行了产前基因诊断。结果96.8％(30／31)SMA患儿携有SMN基因第7外显子缺失。2例产前基因诊断的病例均无SMN基因第7外显子缺失。结论SMN基因缺失检测技术可用于SMA患儿的基因诊断和产前基因诊断。     

应用DHPLC技术检测非缺失型DMD致病基因的新突变

目的建立检测Duchenne型肌营养不良症（Duchenne muscular dystrophy,DMD）致病基因dystrophin突变的快速、敏感的微小突变筛查系统。方法选择经多重PCR检测未发现dystrophin基因大尺度缺失的DMD患儿20例,年龄在2—10岁,以其基因组DNA为模板,通过PCR反应,分别扩增dystrophin基因外显子及侧翼序列,采用变性高效液相色谱（DHPLC）技术进行突变筛查,对DHPLC峰形变异的外显子片段行PCR产物直接测序,确定突变的具体位点和类型。结果筛查了包括2个缺失热点区dystrophin基因的68个外显子和3＇UTR部分片段,分别在4例患儿中检测出该基因的4种致病突变：c．6808_6811delTTHA,c．4959_4960insA,c．8656C〉T和c．8608C〉T。前两例引起移码突变分别导致p．ku2270Metfsx9和p．Ser1654LysfsX5,后两例为无义突变分别导致p．R2886X和p.R2870X。其中c．6808_6811delTTA,c．49594960insA和c．8656C〉T为文献未曾报道的新突变。结论DHPLC可以作为有效地筛查DMD微小突变的检测方法。     

Newborn screening for Duchenne muscular dystrophy (author's transl)

The technique of screening for Duchenne muscular dystrophy (DMD) is a fairly simple procedure. However, the DMD is an untreatable disease. The advantage of screening is only to prevent other cases of DMD by genetic counselling of families to avoid a second, affected child. the estimated effectiveness of the screening is the prevention of 8,3-15% of the hemizygotes. The false negative cases in screening for carrier detection is 30%. (cut-off-level 120 IU/1). Therefore: No screening for carrier detection, voluntary screening in all newborn males and screening in families at risk and in all boys with potential early signs.     

Functional significance of dystrophin positive fibres in Duchenne muscular dystrophy

The age when boys lose the ability to walk independently is one of the milestones in the progression of Duchenne muscular dystrophy (DMD). We have used this as a measure of disease severity in a group of 30 patients with DMD and six patients with intermediate Duchenne/Becker dystrophy (D/BMD). Dystrophin analysis was performed on tissue sections and western blots of muscle biopsy specimens from these patients and the relationships that were found between clinical severity and abundance of dystrophin labelling are reported. All patients with intermediate D/BMD had dystrophin labelling that was detected on sections and blots. Weak dystrophin labelling was found in sections from 21/30 DMD cases and on blots in 18/30 cases. Two non-exclusive patterns of dystrophin labelling were observed on sections: very clear labelling on a small percentage of fibres (usually < 1%) or very weak labelling on a much higher proportion (about 25%). The mean age at loss of mobility among the DMD patients with no dystrophin labelling on tissue sections was 7.9 years (range 6.3-9.5) while the mean age among those with some labelling was 9.9 years (range 8.0-11.9); this is a significant difference. Quantitative estimates of dystrophin abundance were obtained from densitometric analysis of dystrophin bands on blots. In the whole group of 36 patients, a significant positive relationship was found between the abundance of dystrophin and the age at loss of independent mobility. It is concluded that even the very low concentrations of dystrophin found in DMD patients may have some functional significance.     

Functional significance of dystrophin positive fibres in Duchenne muscular dystrophy.

The age when boys lose the ability to walk independently is one of the milestones in the progression of Duchenne muscular dystrophy (DMD). We have used this as a measure of disease severity in a group of 30 patients with DMD and six patients with intermediate Duchenne/Becker dystrophy (D/BMD). Dystrophin analysis was performed on tissue sections and western blots of muscle biopsy specimens from these patients and the relationships that were found between clinical severity and abundance of dystrophin labelling are reported. All patients with intermediate D/BMD had dystrophin labelling that was detected on sections and blots. Weak dystrophin labelling was found in sections from 21/30 DMD cases and on blots in 18/30 cases. Two non-exclusive patterns of dystrophin labelling were observed on sections: very clear labelling on a small percentage of fibres (usually < 1%) or very weak labelling on a much higher proportion (about 25%). The mean age at loss of mobility among the DMD patients with no dystrophin labelling on tissue sections was 7.9 years (range 6.3-9.5) while the mean age among those with some labelling was 9.9 years (range 8.0-11.9); this is a significant difference. Quantitative estimates of dystrophin abundance were obtained from densitometric analysis of dystrophin bands on blots. In the whole group of 36 patients, a significant positive relationship was found between the abundance of dystrophin and the age at loss of independent mobility. It is concluded that even the very low concentrations of dystrophin found in DMD patients may have some functional significance.     

Genetic counseling in X-linked retinitis pigmentosa

The current status regarding genetic counseling in X-linked retinitis pigmentosa (XLRP) is reviewed. XLRP is the most severe form of retinitis pigmentosa (RP) and leads to blindness in the third or fourth decade of life. The biochemical basis of the disease is not known. Until now genetic counseling in this disease has been dependent on simple Mendelian laws of inheritance and the detection of carriers by clinical and electrodiagnostic means. The limitations with regard to carrier detection are discussed. With the recent advances made in recombinant DNA technology, genetic counseling has come to play an important part in the management of XLRP. The methods of DNA technology and their application to localizing the XLRP gene on the X chromosome are reviewed. The discovery of DNA linkage markers known as restriction fragment length polymorphisms (RFLPs) allow a marker closely linked to a disease gene to be followed through succeeding generations in an affected family. Since linkage studies suggest two XLRP loci, carrier detection and prenatal diagnosis of the disease still remain problematic.     

神经源性一氧化氮合酶对临床疑似Becker型肌营养不良的诊断意义

目的：利用免疫组织化学技术检测肌细胞膜上Dystrophin蛋白表达是鉴别诊断Duchenne型和 Becker型肌营养不良（DMD和BMD）的病理学基础，然而个别病例的肌细胞膜上Dystrophin蛋白表达几乎接近于正常，这给临床疑似BMD诊断带来一定困难。本研究探讨神经源性一氧化氮合酶（nNOS）对BMD患者的诊断价值。方法：对 Dys-C 端结构域表达呈阳性的 5 例BMD（其中已临床明确诊断 3 例，临床疑似 2 例）和作为对照的骨折患儿肌肉组织，利用免疫组织化学的方法行单克隆 Dytrophin 抗体和 nNOS 抗体染色。结果：与对照组比较，已临床明确诊断BMD 3例病例的肌细胞膜上 Dys-C、Dys-R 和 Dys-N 端结构域蛋白均有显著缺乏，nNOS 均未见表达；临床疑似 2 例 BMD 病例的肌细胞膜上，即使 Dystrophin蛋白接近于正常表达，但 nNOS 在肌细胞膜上是缺乏的。结论：对 Dystrophinn 三端结构域蛋白接近于正常表达的临床疑似BMD患儿，可通过nNOS抗体染色达到明确诊断的目的。     

假性肥大型肌营养不良的治疗进展

假性肥大型进行性肌营养不良是一类最常见的X 连锁隐性遗传性肌肉疾病,进行性肌无力是主要的临床特征,抗肌萎缩蛋白基因的突变是致病原因。治疗方法一直是研究热点,近年来随着分子生物学诊断治疗技术的日臻成熟,假性肥大型进行性肌营养不良的治疗也有新的突破,该文从传统疗法、基因疗法、细胞移植疗法等方面总结其治疗进展。